The present invention relates, in general, to a crane jib, and more particularly to a crane jib of a type having incorporated therein a device for automatically balancing the crane jib in dependence on the variation of the working radius or reach of the jib.
U.S. Pat. No. 4,867,321, issued Sep. 19, 1989 describes a crane jib of this type which includes a support base for support of a main boom that is rotatable about a vertical pivot axis. The main boom is extendable at one end by an auxiliary boom which is swingable by means of a first adjustment element with respect to the main boom. A counterweight is rotatably supported at the other end of this main boom and swingable by means of a second adjustment element, whereby the adjustment elements are designed as hydraulic cylinders. In order to automatically balance the variation in reach of the auxiliary boom by a change in reach of the counterweight, a connection is provided between the cylinder for pivoting the auxiliary boom and the cylinder for pivoting the counterweight. This conventional crane jib has shortcomings that involve the relatively little use of the applied energy for automatic balancing the variation in reach of the auxiliary boom. Moreover, the stability of the crane deteriorates with increasing reach of the auxiliary boom.